U.S. patent number 7,458,988 [Application Number 10/701,547] was granted by the patent office on 2008-12-02 for compressible corpectomy device.
This patent grant is currently assigned to Warsaw Orthopedic, Inc.. Invention is credited to Bret M. Berry, Michael C. Sherman, Hai H. Trieu.
United States Patent |
7,458,988 |
Trieu , et al. |
December 2, 2008 |
Compressible corpectomy device
Abstract
A vertebral implant device for interposition between two
vertebral endplates comprises an outer body and an inner body. The
outer body movably engages the inner body. A core member positioned
between the outer body and the inner body is at least partially
compressed when a load is applied to the implant device.
Inventors: |
Trieu; Hai H. (Cordova, TN),
Sherman; Michael C. (Memphis, TN), Berry; Bret M.
(Jacksonville, FL) |
Assignee: |
Warsaw Orthopedic, Inc.
(Warsaw, IN)
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Family
ID: |
34551451 |
Appl.
No.: |
10/701,547 |
Filed: |
November 5, 2003 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050096744 A1 |
May 5, 2005 |
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Current U.S.
Class: |
623/17.13 |
Current CPC
Class: |
A61F
2/4611 (20130101); A61F 2/44 (20130101); A61F
2002/30566 (20130101); A61F 2310/00161 (20130101); A61F
2310/00203 (20130101); A61F 2002/30616 (20130101); A61F
2310/00029 (20130101); A61F 2002/2835 (20130101); A61F
2002/30604 (20130101); A61F 2002/30904 (20130101); A61F
2002/30584 (20130101); A61F 2/441 (20130101); A61F
2002/30187 (20130101); A61F 2002/4628 (20130101); A61F
2220/0033 (20130101); A61F 2230/0034 (20130101); A61F
2310/00239 (20130101); A61F 2002/2817 (20130101); A61F
2002/30133 (20130101); A61F 2002/30601 (20130101); A61F
2002/30841 (20130101); A61F 2002/30795 (20130101); A61F
2002/30563 (20130101); A61F 2002/30004 (20130101); A61F
2310/00023 (20130101); A61F 2310/00131 (20130101); A61F
2002/30892 (20130101); A61F 2230/0015 (20130101); A61F
2002/30685 (20130101); A61F 2002/30369 (20130101); A61F
2310/00293 (20130101); A61F 2310/00017 (20130101); A61F
2002/30593 (20130101); A61F 2002/30922 (20130101); A61F
2/30767 (20130101); A61F 2310/00167 (20130101); A61F
2310/00329 (20130101); A61F 2002/30784 (20130101); A61F
2250/0014 (20130101); A61F 2002/30733 (20130101); A61F
2002/3082 (20130101); A61F 2002/30777 (20130101) |
Current International
Class: |
A61F
2/44 (20060101) |
Field of
Search: |
;623/17.11-17.16 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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20019520 |
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Feb 2001 |
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DE |
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0277282 |
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Aug 1988 |
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EP |
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0 950 389 |
|
Oct 1999 |
|
EP |
|
Other References
Patent Cooperation Treaty--European Patent Office, "Notification of
Transmittal of The International Search Report and The Written
Opinion of the International Searching Authority, or the
Declaration," Jun. 2, 2005, 18 pages. cited by other.
|
Primary Examiner: Snow; Bruce E.
Attorney, Agent or Firm: Haynes and Boone, LLP
Claims
What is claimed is:
1. A vertebral implant device for interposition between two
vertebral bodies, the device comprising: an outer body including a
chamber and a first vertebral interface endwall textured for
engagement with one of the two vertebral bodies; an inner body
including a second vertebral interface endwall textured for
engagement with the other of the two vertebral bodies, wherein the
outer body includes at least one slot and the inner body includes
at least one tab, and wherein the tab movably engages the slot; and
a core member positioned entirely within the chamber, wherein the
outer body is movably engaged with the inner body and wherein
responsive to a load applied to the device, the outer and inner
body at least partially compress the core member and, wherein the
outer body and inner body each comprise a cavity for containing
bone growth promoting material.
2. The vertebral implant device of claim 1 wherein the inner body
comprises a shaft extending at least partially into the
chamber.
3. The vertebral implant device of claim 2 wherein responsive to
the load applied to the device, the shaft slidably advances into
the chamber causing the at least partial compression of the core
member.
4. The vertebral implant device of claim 1 further comprising a
longitudinal axis, wherein the slot extends longitudinally along
the outer body and the tab translates within the slot for movably
engaging the outer and inner bodies.
5. The vertebral implant device of claim 1 wherein the tab prevents
the inner body from disengaging the outer body.
6. The vertebral implant device of claim 1 wherein the outer body
comprises one or more apertures in communication with the
cavity.
7. The vertebral implant device of claim 1 wherein the outer body
includes a longitudinal axis and an end portion extending at a
non-perpendicular angle with respect to the longitudinal axis.
8. The vertebral implant device of claim 1 wherein the inner body
includes a longitudinal axis and an end portion extending at a
non-perpendicular angle with respect to the longitudinal axis.
9. The vertebral implant device of claim 1 wherein the device
includes a substantially oval cylindrical cross-section.
10. The vertebral implant device of claim 1 wherein the core member
comprises one or more compartments.
11. The vertebral implant device of claim 1 wherein the core member
comprises an elastomer.
12. The vertebral implant device of claim 11 wherein the elastomer
comprises polyurethane.
13. The vertebral implant device of claim 11 wherein the elastomer
comprises silicone.
14. The vertebral implant device of claim 11 wherein the elastomer
comprises a copolymer of polyurethane and silicone.
15. The vertebral implant device of claim 11 wherein the elastomer
comprises polyolefin rubber.
16. The vertebral implant device of claim 1 wherein the core member
comprises a hydrogel.
17. The vertebral implant device of claim 16 wherein the hydrogel
comprises a polyvinyl alcohol hydrogel.
18. The vertebral implant device of claim 16 wherein the hydrogel
comprises a polyacrylonitrile-based hydrogel.
19. The vertebral implant device of claim 16 wherein the hydrogel
comprises a polyacrylic-based hydrogel.
20. The vertebral implant device of claim 16 wherein the hydrogel
comprises a polyurethane-based hydrogel.
21. The vertebral implant device of claim 1 wherein the core member
comprises one or more polymers.
22. The vertebral implant device of claim 1 wherein the core member
comprises one or more surface features for altering the response of
the core member to the at least partial compression.
23. The vertebral implant device of claim 1 wherein the core member
comprises one or more subsurface features for altering the response
of the core member to the at least partial compression.
Description
FIELD OF THE INVENTION
The present invention relates generally to an implant for
replacement of one or more vertebral bodies and their adjacent
discs, and more particularly, to a vertebral implant assembly
having a compressible core component.
BACKGROUND
A variety of spinal injuries and deformities can occur due to
trauma, disease, or congenital effects. These injuries and diseases
can, ultimately, result in the destruction of one or more vertebral
bodies and lead to a vertebrectomy or corpectomy in which the one
or more damaged vertebral bodies and their adjacent discs are
excised. Reconstruction of the spine following the vertebrectomy
can present a number of challenges for the surgeon.
One surgical concern is securely interposing a vertebral implant
between the remaining rostral and caudal vertebral bodies to allow
the implant to resist dynamic loads, including axial, torsional,
and shear loading, without undue subsidence or damage to the
adjacent vertebral endplates. Therefore, a vertebral implant
assembly is needed that can be installed with minimal injury to
surrounding structures and that comprises durable components for
dampening the affect of dynamic loading on the spine.
SUMMARY
This invention relates to a vertebral implant device for
interposition between two vertebral endplates. The device comprises
an outer body, an inner body, and a core member positioned between
the outer body and the inner body. The outer body may be movably
engaged with the inner body. Responsive to a load applied to the
device, the outer and inner body may at least partially compress
the core member.
In another embodiment, a vertebral implant device configured for
interposition between two vertebral endplates comprises first and
second outer bodies, a center shaft, and first and second core
members. The first core member is positioned between the first
outer body and the center shaft, and the second core member is
positioned between the second outer body and the center shaft. The
outer bodies may be movably engaged with the center shaft.
Responsive to a load applied to the device, the outer bodies and
the center shaft may at least partially compress the core
members.
In still another embodiment, a vertebral implant device is
installed between two vertebral endplates in a vertebral column
using a method of the present invention. A core member may be
positioned within an outer body of the device. The outer device may
be placed in movable engagement with the inner body of the device
with the core member positioned between the inner body and the
outer body. An insertion instrument may be used to compress the
device and position the device in the vertebral column.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a destroyed vertebral body within a
vertebral column.
FIG. 2a is an exploded perspective view of a vertebral implant
assembly according to one embodiment of the present invention.
FIG. 2b is a perspective view of the assembled implant assembly of
FIG. 2a.
FIG. 3 is a cross sectional view of the implant assembly of FIG.
2a.
FIG. 4 is a top view of the implant assembly of FIG. 2a.
FIG. 5 is a cross sectional view of the core member of FIG. 2a.
FIG. 6 is a perspective view of a vertebral implant assembly with
an installation device.
FIG. 7 is an exploded perspective view of a vertebral implant
assembly according to a second embodiment of the present
invention.
FIG. 8 is a perspective view of the assembled implant assembly of
FIG. 6.
DETAILED DESCRIPTION
For the purposes of promoting an understanding of the principles of
the invention, reference will now be made to the embodiments, or
examples, illustrated in the drawings and specific language will be
used to describe the same. It will nevertheless be understood that
no limitation of the scope of the invention is thereby intended.
Any alterations and further modifications in the described
embodiments, and any further applications of the principles of the
invention as described herein are contemplated as would normally
occur to one skilled in the art to which the invention relates.
Referring first to FIG. 1, the reference numeral 10 refers to a
vertebral column with a damaged vertebra 12a extending between two
intact vertebrae 12b and 12c. An intervertebral disc 14a extends
between vertebral bodies 12a and 12b, and an intervertebral disc
14b extends between vertebral bodies 12a and 12c. In a typical
surgical excision, the vertebra 12a is removed together with discs
14a and 14b creating a void between the two intact vertebra 12b and
12c. This procedure may be performed using an anterior,
anterolateral, or other approach known to one skilled in the art. A
vertebral implant assembly according to an embodiment of the
present invention is then provided to fill the void between the two
intact vertebrae 12b and 12c. Although the embodiment to be
described is premised upon the removal of a single vertebra, it is
understood that a different embodiment of the present invention may
be inserted in an intervertebral disc space without the removal of
a vertebrae when required by the surgical procedure. In still
another embodiment, the present invention may be used in a
vertebral column reconstruction following a vertebrectomy removing
two or more diseased or damaged vertebrae and their adjacent
discs.
Referring now to FIG. 2a, a vertebral implant device according to
an embodiment of the present invention is referred to, in general,
by the reference numeral 20 and includes an outer body 22 and an
inner body 24 between which a core member 26 may be positioned.
FIG. 2b illustrates the components of FIG. 2a in an assembled
condition in preparation for implantation in a vertebral column as
will be described in detail below.
Referring now to FIG. 3, the outer body 22, includes a lateral wall
28 and an endwall 30. In one embodiment, endwall 30 includes a
cavity 32 configured to accept bone growth promoting substances
such as, but without limitation, bone graft material, bone
morphogenetic protein (BMP), or other osteoinductive or
osteoconductive material (not shown). To promote a secure and
stabile interface between the implanted device 20 and the adjacent
vertebrae in the vertebral column, one or more apertures 34 may
preferably extend from the cavity 32 through the lateral wall 28,
permitting bone growth in and around the outer body. The apertures
34 may further permit the movement of fluid into and out of the
cavity 32. Although the apertures 34, as depicted in FIG. 3, may be
directed away from the endwall 30, it is understood that they may
be directed in any of a variety of orientations based upon the
surgical application, the material used, or other design
factors.
A plurality of protrusions 36 or other surface roughening may be
formed on the endwall 30 to restrict movement of the implanted
device 20. In some embodiments, the protrusions 36 may be
relatively low ridges or textured areas on the endwall 30 which are
adapted to engage the endplate of the adjacent vertebral body to
maintain the position of the implanted assembly. In other
embodiments, the protrustions 36 may be longer, cleat-like
structures, which can penetrate the endplate of the adjacent
vertebra to hold the implanted assembly in place. The endwall 30
may also or alternatively comprise one or more grooves 38
configured to accept the prongs of a compression and/or insertion
instrument.
As shown in FIG. 3, the endwall 30 may be perpendicular to a
longitudinal axis 40 of the of the outer body 22. However, in an
alternative embodiment, the endwall 30 may form any of a variety of
angles relative to the longitudinal axis 40 to accommodate a
particular patient anatomy or to achieve a desired alignment. It
will be appreciated that in certain regions of the spine, the
vertebral endplates are disposed in a non-parallel relationship to
establish kyphosis or lordosis. Although the outer body 22 may be
generally cylindrical, as shown in FIG. 4, it can include curved or
flat areas which allow the outer body 22 to more closely match the
profile of the adjacent vertebra after surgical implantation. The
outer body 22 may be formed in a variety of heights and widths and
with a variety of endwall angulations. For example, the outer body
22 may have a height of approximately 32 mm. and an endwall
angulation of 2.degree.. A cross section of the outer body 22
perpendicular to the longitudinal axis 40 may have any of a variety
of geometries and in certain embodiments may correspond to a cross
section of the core member 26.
The outer body 22 may comprise an endwall 42 opposite the endwall
30. Through this endwall 42 a chamber 44, having chamber walls 45
and a chamber base 46, may be formed for housing the core member 26
and at least a portion of the inner body 24. In certain
embodiments, the chamber 44 has smooth chamber walls 45 which curve
into the chamber base 46. The smooth walls 45 can minimize abrasion
which can damage the core member 26. The chamber 44 may conform
closely to the shape of the core member or alternatively, may be
shaped to comprise depressions, recessed areas, or other geometries
into which the core member 26 may deform when subjected to
loading.
An elongated slot 48 (see also FIGS. 2a and 2b) may extend
longitudinally along the wall 28 of the outer body 22. The
elongated slot 48 may extend through the wall 28 and in
communication with the chamber 44. In an alternative embodiment,
the slot 48 may extend only partially through the wall 28 without
penetrating the exterior of the outer body 22. As will be described
below, the slot 48 may be a retaining member used to connect the
outer body 22 to the inner body 24. In an alternative embodiment,
the outer body 22 may have a plurality of slots 48.
An aperture 49 may also extend through the wall 28 of the outer
body 22 in communication with the chamber 44. In certain
embodiments, a plurality of apertures 49 may extend through the
wall 28. The aperture 49 may permit the evacuation of fluids or
other material which may seize or otherwise restrict the smooth
transition between the outer body 22 and the inner body 24
Referring still to FIG. 3, the inner body 24 may include an endwall
50 having a cavity 52, apertures 54, grooves 56, and protrustions
58 all configured similarly or identical to the corresponding
structures of the outer body 22. As described above for the endwall
28, the endwall 50 may be angled to accommodate a particular
patient anatomy or to achieve a desired vertebral alignment. A
cross section of the inner body 24 perpendicular to the
longitudinal axis 40 may have any of a variety of geometries and in
certain embodiments may correspond to a cross section of the core
member 26. Extending along the longitudinal axis 40 away from the
endwall 50, a shaft 60 is configured to engage at least a portion
of the chamber 44 of the outer body 22. Although the shaft portion
60 of the inner body 24 may be solid, in an alternative embodiment,
the cavity 52 may extend into the shaft 60.
Opposite the endwall 50, the inner body 24 comprises an endwall 62
having a surface substantially perpendicular to longitudinal axis
40. Endwall 62 may be shaped to conform to the contours of core
member 26. The shaft 60 may further comprise a laterally extending
retaining tab 64 configured to slidably engage the slot 48 of the
outer body 22. The tab 64 may permit slidable movement while
retaining the inner body 24 and preventing the inner body 24 from
disengaging the outer body 22. Where the outer body 22 comprises a
plurality of slots 48, the shaft 60 may comprise a corresponding
plurality of tabs 64. The tabs may, alternatively, be formed on the
outer body 22 to engage slots formed on the inner body 24.
The shaft 60 may, for example, be formed as an oval cylinder or
another shape that can prevent rotational movement of the inner
body 24 when positioned within the chamber 44 of the outer body 22.
Although depicted as a right cylinder, in an alternative
embodiment, the shaft 60 may have angled walls to permit limited
pivoting of the inner body 24 with respect to the longitudinal axis
40 without allowing the bodies 22 and 24 to become detached. In
some embodiments, the shaft 60 may fit snugly within a portion of
the chamber 44, in others, the fit may be somewhat loose, allowing
play between the bodies 22 and 24. The inner body 24 may be formed
in a variety of heights and widths and with a variety of endwall
angulations. For example, the outer body 22 may have a height of
approximately 29 mm. and an endwall angulation of 2.degree..
The outer body 22 and the inner body 24 may be formed from a
biocompatible material suitable to withstand the application of
external compressive, axial, torsional, and bending loads, as well
as strong enough to provide support for the adjacent intact
vertebrae. The outer and inner bodies may be formed from the same
or different materials. Suitable materials may have a higher
modulus than the core member 26. Suitable biocompatible materials
may include metals such as titanium, titanium alloys, cobalt-chrome
alloys, titanium nickel alloys, and surgical grade stainless steel.
Suitable polymers may include ultra-high molecular weight
polyethylene, polyaryletherketone, ployetheretherketone, polymethyl
methacrylate, polyacetal, polysulfone, and polyimide. Suitable
ceramic materials may include alumina, zirconia, polycrystalline
diamond compact, pyrolitic carbon, and a porous tantalum material
such as HEDROCEL.RTM. provided by Implex Corporation of Allendale,
N.J. Suitable composite materials may include carbon-filled
composites, hydroxyl-appetite-filled composites, and
bioactive-glass-filled composites. A combination of any of the
above materials may also be used.
The surfaces of the bodies 22 and 24 may be modified to suit
particular purposes. For example, surfaces intended to contact bone
may be roughened, textured, spiked, serrated, or coated with
osteoconductive materials such as calcium phosphate or hydroxyl
appetite. Surfaces of bodies 22 and 24 which may contact the core
member 26 may be smooth, hardened, and/or lubricated for lowering
friction and reducing wear and tear on the core member.
Referring still to FIG. 3, the core member 26 is configured to
occupy at least a portion of the chamber 44 between the chamber
base 46 and the endwall 62 of the inner body 24. The core member 26
may be formed from a homogenous and/or semi-solid material which
may be inserted or injected into the cavity 40. Suitable materials
may include one or more materials such as plastics, rubbers,
elastomers, hydrogels, or other combinations.
Core member 26 may also be comprised of a copolymer, a blend, a
composite, or a laminate of various polymers. Examples of
copolymers include a copolymer of polyether urethane and silicone
or a copolymer of polycarbonate urethane and silicone. An example
of a blend includes a blend of the copolymers described above.
Examples of a composite include polyester fabric or fibers in
silicone-polyether urethane. One example of a laminate is multiple
layers of silicone-polyether urethane and polyester fabric or
polyethylene mesh. Another example of a laminate is multiple layers
of hydrogel and polyester mesh.
The core member 26 may be comprised of an elastomer or any other
flexible material capable of recovering at least some amount of its
original size and shape after deformation. Suitable materials may
include polyurethane, copolymers of silicone and polyurethane,
silicones, polyolefin rubbers, polyvinyl alcohol hydrogels,
polyacrylonitrile-based hydrogels, polyacrylic-based hydrogels, and
polyurethane-based hydrogels.
Alternatively, the core member 26 may comprise a membrane or casing
formed from an elastomer material and having one or more
compartments filled with a hydrogel, an elastomer, a liquid, a
gaseous substance, or any other appropriate material. In some
embodiments the material or materials used to form the core member
26 may result in a compressible core member, but in certain other
embodiments, the core member may be relatively rigid, functioning
as a strut between outer body 22 and inner body 24.
As shown in FIGS. 2a and 5, the core member 26 may be formed having
grooves 65a, apertures 65b (which may be vertical, horizontal or
angled), or other features including indentions, isolated voids,
interconnected voids which can modify the characteristics of the
core member 26 such as stiffness, compliance, shock absorption,
compression resistance and other characteristics that affect stress
relief and enhance the device's 20 absorbtion of dynamic loads. The
features may be located on or below the surface of the core member
26. In alternative embodiments, the core member 26 may have a
smooth, uniform surface. As shown in FIG. 5, the cross section of
the core member 26 may be generally oval. It is understood,
however, that the shape of the core member 26 may be selected to
conform to the shape of the chamber 44 or to the deformation
requirements of the vertebral implant device 20. The geometry of
the core member cross section may be round, rectangular, square,
elliptical, hexagonal or any other shape useful to a particular
application. In some embodiments the physical structure of the core
member 26, for example a spring or coil shape, may provide the
elasticity to absorb the loads applied to the device 20. The core
member 26 may be a single structure or may comprise one or more
discrete structures capable of being housed in the chamber 44.
As shown in FIGS. 3 and 4, the components of implant device 20 may
be assembled prior to implantation. For example, the core member 26
may be inserted into the cavity 44 of the outer body. Next, tab 64
of the inner body can engage the slot 48 of the outer body 22
thereby connecting the outer body 22 to the inner body 24 and
containing the core member 26 between the two bodies. The tab 64
may be permitted to move within the slot 48 thus permitting
movement of the inner body 24 along the longitudinal axis 40
without allowing the bodies 22 and 24 to disengage. Both the shape
of the bodies 22 and 24 and the configuration of the slot 48 and
tab 64 may restrict rotational movement, ensuring that motion is
limited to axial translation. It is understood that multiple tabs
and slots can be used to achieve this same type of movement. With
the tab 64 translating within the slot 48, the core member 26 may
compress or expand as the size of the space between the cavity base
46 and the endwall 52 is varied by external forces.
Following the corpectomy removing vertebra 12a, for example, the
space may be evaluated to determine the correct size and endplate
orientation. If modular components are available, a care giver may
select the components having the size, shape, and angle best suited
to fit the space and to accommodate the requirements of a
particular patient. Further, the core elasticity may be selected to
correspond to patient weight or desired spinal loads to best suit
the prosthesis to the patient. In some embodiments the components
may be assembled in the surgical arena, and in other embodiments,
the components may be pre-assembled in a factory or in another
facility which pre-assembles and distributes assembled components
to care providers.
The pre-assembled implant device 20 may be inserted into the
vertebral column 10 between the remaining vertebrae 12b and 12c.
Before insertion, each of the cavities 32 and 52 may be packed with
bone growth promoting material to facilitate bone growth and
stability of the implanted device 20. The device 20 may be oriented
such that the outer body 22 is in the rostral position, but in an
alternative embodiment, the inner body 24 may be in the rostral
position.
Referring now to FIG. 6, in one embodiment, the device 20 may be
compressed during installation to permit insertion of the device 20
without damaging the adjacent vertebrae. The maximum compression of
the device 20 may be limited by several features of the device 20
including the elasticity of the core member 26, the length and
position of the slot 48, and the size of the chamber 44. An
insertion instrument 66 may be used to facilitate installation of
the implant device 20. The insertion instrument 66 may, for
example, engage the grooves 38 and 56 of the bodies 22 and 24 with
prongs 68 which can apply a compressive force for compacting the
device 20. One embodiment of the insertion instrument 66 is
disclosed in U.S. patent application Ser. No. 10/441,689 which is
incorporated by reference herein. When the device 20 is
sufficiently compacted to permit installation in the space between
the vertebrae 12b and 12c, the insertion instrument 66 can be used
to move the device 20 into place. After the device 20 is positioned
within the spinal column 10, the prongs 68 of the insertion
instrument 66 may be extracted.
Once located in the space vacated by vertebra 12a, the device 20
may be allowed to expand to occupy the space. In some embodiments,
however, the core member can remain under at least some amount of
compression after the device 20 is located in the vertebral column
and allowed to expand. After expansion, the endwall 30 can engage
the endplate of vertebra 12b, and the endwall 50 can engage the
endplate of the vertebra 12c. Specifically, the protrusions 36 may
press against the adjacent vertebral endplates, mechanically
holding the device 20 in place. Additionally or alternatively, the
bodies 22 and 24 may be fused to the adjacent vertebrae through
bone ingrowth into the upper and lower cavities. Alternatively, the
bodies 22 and 24 may be cemented or chemically bonded with other
methods known in the art. The compressive forces exerted by the
adjacent vertebrae 12b and 12c on the device 20 may further operate
to ensure a consistent, intimate contact between the device and the
vertebrae. If necessary, after installation additional bone growth
promoting material may be inserted into the cavities 32 and 52
through the apertures 34 and 54.
In certain embodiments, the device 20 may be inserted into the
vertebral column without first compressing the device. In such an
embodiment, following the removal of the vertebra 12a, the
remaining vertebrae 12b and 12c may be distracted to maintain or
increase the separating space. The device then be installed without
compression.
After installation, the elasticity of the core member 26 and the
limited movement of the translatable inner body 24 can permit
movement within the device 20 to dissipate dynamic loads, thereby
reducing the risk of subsidence and other forms of damage to the
remaining vertebrae and discs in the vertebral column 10. The shape
of the cavity 44, the configuration of the core member 26, and the
amount of play between the outer body 22 and the inner body 24 can
allow the vertebral implant device 20 to accommodate aligment
imperfections. Over time, the outer body 22 and inner body 24 may
settle into their adjacent vertebral endplates, increasing the
spacing between the vertebral endplates. Embodiments in which the
core member 26 is held in compression after installation
accommodate this settlement by allowing the core member 26 to
continue exerting pressure on the bodies 22 and 24 to maintain good
anchorage and to promote fusion.
Referring now to FIG. 7, in another embodiment of the present
invention, the implant device 20 includes the outer body 22, the
core member 26, a second outer body 70, a second core member 72 and
a center shaft 74. The second outer body 70 and the second core
member 72 may be similar or identical to the outer body 22 and the
core member 26, respectively, and therefore, these components will
not be described in detail except to define a chamber 76 and a slot
78 in the second outer body 70 which correspond to the chamber 44
and the slot 48, respectively. The center shaft 74 extends between
the core member 26 and the core member 72. The center shaft 74
comprises an end portion 80 configured to engage chamber 44 and an
end portion 82 configured to engage cavity 76. End portion 80 may
include a laterally extending tab 84 configured to slidably engage
the slot 48 of the outer body 22. The end portion 82 may also
include a laterally extending tab 86 configured to slidably engage
the slot 78 of the second outer body 70. Where the outer bodies 22
and 70 comprise a plurality of slots, the center shaft 74 may
comprise a corresponding plurality of tabs.
Referring now to FIG. 8, The device 20 may be preassembled such
that the core member 26 is positioned within the chamber 44, and
the core member 72 is positioned within the chamber 76. The tab 84
of the center shaft 74 may engage slot 48 and the tab 86 may engage
slot 78, thereby containing the core members 26 and 72 within the
respective chambers. The device 20 may be installed in a manner
similar to that disclosed above. After installation, the
translatable center shaft 74 and the pair of core members 26 and 72
allow the device 20 to dampen dynamic loads applied to the
vertebral column.
It is understood that particular features of the center shaft 74
and the outer bodies 22 and 70 may be interchanged. For example,
the center shaft 74 may incorporate chambers for housing the core
members, in which case, the outer bodies 22 and 70 may comprise
shaft portions configured to engage the cavities of the center
shaft. The center shaft 74 may further include slots configured to
engage tabs located on the outer bodies 22 and 70.
To accommodate a variety of surgical applications, the device 20
may include multiple center shafts and more than two core members.
It is understood that the various features of the center shafts and
outer bodies may be interchanged to achieve the coupling of
multiple components.
Although only a few exemplary embodiments of this invention have
been described in detail above, those skilled in the art will
readily appreciate that many modifications are possible in the
exemplary embodiments without materially departing from the novel
teachings and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of this
invention as defined in the following claims. In the claims,
means-plus-function clauses are intended to cover the structures
described herein as performing the recited function and not only
structural equivalents, but also equivalent structures.
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